Contactless web turning guides are employed for the guidance of webs of paper and similar materials, to effect a change in the direction of the web without permitting the web to make contact with a solid surface. In general, such a turning guide has an arcuate guide surface which is convexly curved along the direction of movement of the web and which the web follows to undergo change of direction. Pressure air outlets at various locations in or adjacent to the guide surface maintain pressure air between that surface and the web, so that the web floats on a film of air that keeps it spaced from the guide surface even as it closely follows the guide surface curvature.
One form of contactless web turning guide is disclosed in the allowed copending application of Robert A. Daane, Ser. No. 937,468, filed Aug. 28, 1978 (now U.S. Pat. No. 4,197,972 issued Apr. 15, 1980) which has a common assignee herewith. In the guide there disclosed, the web was floated on pressure air issuing from air nozzles under the web that extended across substantially the full width of the web and were spaced from one another around the curved guide surface. In addition, a stream of air was directed towards each edge of the web from an elongated edge-jet air outlet that was spaced a little distance outwardly from each edge of the web and extended parallel to the web edge. The air stream blown from each of these edge-jet outlets retarded the outflow of pressure air from under the web and also acted on the web to confine it against edgewise side drift.
Although this prior arrangement was by no means unsuccessful or unsatisfactory, the present invention has resulted from efforts to achieve substantial improvements in it, particularly with respect to reducing the energy that it consumes for supplying pressure air and increasing the stability of the moving web in the portion of its path that is defined by the turning guide.
In initial efforts to achieve these objectives, the elongated edge-jet outlets that were located in outwardly spaced relation to the web were replaced by similar outlets located just under the web, near its side edges, each discharging air in a laterally inward direction relative to the web. Such air outlets were found not to provide sufficient support under the marginal portion of the web, with the result that there was folding down and dragging of the web edge.
The present invention involves the surprising discovery that two properly arranged elongated edge-jet air outlets at each side of the web, instead of the single such outlet heretofore used, will materially reduce pressure air requirements instead of having the expectable result of increasing the requirements for pressure air, and, moreover, will bring about greatly improved web stability and web tracking.
Thus the general object of the present invention is to provide an improved web turning guide for contactlessly supporting and guiding a web around an arcuate turn in a portion of a defined path along which the web extends and runs, and particularly to provide an improved arrangement of air jet outlets for such a web turning guide whereby substantially less energy is needed for operation of the web turning guide and whereby better tracking and guidance and more stable running of the web is obtained.
It is also an object of this invention to provide a contactless web turning guide that is readily adaptable for cooperation with a web of any of several different widths and which requires a relatively small quantity of pressure air at a relatively low pressure for maintaining a flotation film between the web guide surfaces and a web but nevertheless affords excellent tracking and very stable running of the web, with very uniform pressure air support of the web all across its width and around the curve defined by the turning guide.